Known coaxial waveguide elbows consist of a set of two symmetrical circular elements, affixed at right angles to form an elbow, with a flattened junction, as shown in FIGS. 1A-1E, which bridge a corner between two coaxial waveguide structures which also intersect at right angles. The electromagnetic waves are thus transduced by the circular elements between waves traveling at right angles.
The Electronics Industry Association has promulgated standard RS-225, which defines certain gas-insulated coaxial transmission lines, which have been extended by the industry to encompass a broad range of sizes, with standard impedances including 50.OMEGA., 75.OMEGA. and 100.OMEGA., and specialty structures ranging from 35.OMEGA. to 200.OMEGA.. Such coaxial transmission lines are available in a broad range of sizes, for example from 7/8 inch to 24 inch diameter, and used for frequencies from DC up to about 3 GHz. These gas-insulated transmission lines shall be referred to herein as "EIA-type" coaxial transmission lines.
It has been found, however, that the standard miter arrangement of circular elements for traversing corners is not entirely satisfactory. The elbow structure is very sensitive to variations, such as concentricity, thermal expansion, surface irregularities, and the like, making tuning difficult and resulting in variations in loss and reflections, e.g., VSWR. The structure also has a narrow bandwidth and considerable loss factor.
In these known structures, the circular elements have 45.degree. double-bevels, forming a right angle between the circular elements, and having an ellipsoidal flat face having an eccentricity of 1.414 (.sqroot.42) opposite the right angle junction.
An alternative known method of redirecting electromagnetic waves in a coaxial waveguide provides a coaxial structure with a gradual sweep bend, i.e. forming a section of a toroidal structure for the inner conductor. While this provides good electrical properties, it may require a significant distance to turn a right angle, and may be difficult to fabricate and install. Precise adjustments of such a structure are also difficult, due to the curved shape.